1. Field of the Invention
The present invention relates to a circuit for driving a linear compressor enabling to reduce a cost in detecting voltage and current applied to a linear compressor by decreasing the number of precision resistors.
2. Background of the Related Art
Generally, a linear compressor having no crankshaft transforming a rotary motion into a straight-line motion enables to reduce its frictional loss, thereby being superior to other compressors in efficiency. And, the linear compressor variously transforms a voltage corresponding to a stroke applied to the linear compressor to vary a compression ratio. Therefore, the linear compressor is used for a variable cooling capacity control for a refrigerator, an air conditioner and the like.
FIG. 1 illustrates a circuit for driving a linear compressor according to related art.
Referring to FIG. 1, a circuit for driving a linear compressor according to related art includes a linear compressor 10A controlling a cooling capacity (endothermic heat from surroundings during evaporation for a cooling operation as a material of 1 Kg passes through an evaporator) by varying a stroke(a distance from one end to the other end of a piston) through an up-and-down rectilinear motion of a piston, an electric circuit unit 10 controlling a current applied to the linear compressor 10A by connecting a ground terminal between a current detect resistance R1 and a triac Tr1 and by shorting or disconnecting an alternating current in accordance with a switching signal of the triac Tr1, a current detection unit 20 detecting a current applied to the linear compressor 10A and outputting the detected current, a voltage detection unit 30 receiving a voltage between two ends of the linear compressor 10A to amplify differentially using a differential amplifier 30A and including a level shifter 30B carrying out a level shifting, a stroke calculation unit 40 receiving the detected current and voltage from the current and voltage detection units 20 and 30 and calculating a stroke of the linear compressor 10A, and a microcomputer 50 comparing the stroke calculated by the stroke calculation unit 50 to an initial stroke reference and then supplying the electric circuit unit 10 with a switching signal for controlling a voltage applied to the linear compressor 10A in accordance with a difference between the calculated stroke and initial stroke reference.
The voltage detection unit 30 includes a couple of OP amplifiers, in which a negative voltage terminal of the linear compressor 10A is connected to an inversion terminal (xe2x88x92) of the differential amplifier 30A through a precision resistor Ra1, a positive voltage terminal of the linear compressor 10A is connected to a non-inversion terminal(+) of the differential amplifier 30A through a precision resistor Ra2 and a precision resistor Ra3 of which one end is grounded, a precision resistor Ra4 is connected between an output terminal of the differential amplifier 30A and the inversion terminal(xe2x88x92) of the differential amplifier 30A, the output terminal of the differential amplifier 30A is connected to an inversion terminal(xe2x88x92) of the level shifter 30B through a precision resistor Ra5, a power voltage supply of 5 V is inputted to the level shifter 30B through a precision resistor Ra6 and a precision resistor Ra7 of which one end is grounded, and another precision resistor is connected between an output terminal and the inversion terminal(xe2x88x92) of the level shifter 30B.
Operation and effect of the circuit for driving the linear compressor according to the related art are explained by referring to the attached drawing as follows.
A normal AC alternating current power supply voltage of 220 V is applied to the linear compressor 10A through a current detect resistor R1, the triac Tr1, and a capacitor C. Thus, a current flows through the linear compressor 10A and a piston of the linear compressor 10A carries out a straight-line reciprocation motion by the current. The straight-line reciprocation determines a stroke as a straight-line reciprocation distance of the piston. Thus, the cooling capacity is controlled by varying the stroke.
In this case, the current detection unit 20 detects a current applied to the linear compressor 10A through the current resistor R1 and then inputs the detected current to the stroke calculation unit 40. The voltage detection unit 30, when the linear compressor 10A is driven, detects a voltage between both ends of the linear compressor 10A to input the voltage to the stroke calculation unit 40. In this case, the voltage between both ends of the linear compressor 10A is amplified by the differential amplifier 30A through two precision resistors R1 and R2. The value amplified by the differential amplifier 30A is then compared to the power supply voltage of 5 V by the level shifter 30B to be detected. Successively, the stroke calculation unit 40 receives the current and voltage detected from the linear compressor 10A to calculate the stroke, and then inputs the calculated stroke value to the microcomputer 50. The microcomputer 50 adjusts the voltage to be applied to the linear compressor 10A using a speed peak control algorithm stored previously in a memory of the microcomputer 50. Namely, the microcomputer 50 compares the stroke calculated by the stroke calculation unit 40 to the initial stroke reference. If the calculated stroke value is higher than the initial stroke reference, the microcomputer 50 outputs the switching signal turning off the triac Tr1 as an AC switching device of the electric circuit unit 10 to reduce the voltage applied to the linear compressor 10A.
On the other hand, if the calculated stroke, i.e. the present stroke, is lower than the initial stroke reference, the microcomputer 50 outputs the other switching signal turning on the triac Tr1 as an AC switching device of the electric circuit unit 10 to increase the voltage applied to the linear compressor 10A.
After all, through the two processes, the microcomputer 50 inputs the switching signal enabling to adjust the voltage applied to the linear compressor 10A to the triac Tr1 to make the present stroke follow the initial stroke reference.
Unfortunately, the circuit for driving the linear compressor according to the related art has to detect the voltage and current of the linear compressor using a plurality of the precision resistors to calculate a precise senseless stroke. Therefore, the circuit of the related art has to use the expensive precision resistors, thereby being unable to avoid increasing a product cost.
Accordingly, the present invention is directed to a circuit for driving a linear compressor that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a circuit for driving a linear compressor enabling to reduce its product cost by reducing the number of precision resistors and using a ground terminal in common for detecting voltage and current of a linear compressor.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a circuit for driving a linear compressor according to the present invention includes a liner compressor controlling a cooling capacity by varying a stroke through an up-and-down straight-line motion of a piston, an electric circuit unit supplying the linear compressor with voltage and current in accordance with a switching signal of an AC switching device through a current detect resistor and the AC switching device wherein a ground terminal is connected between the current detect resistor and linear compressor, a voltage detect unit detecting the voltage applied to the linear compressor by taking the ground terminal as a reference and outputting the detected voltage, a stroke calculation unit receiving the detected current and voltage to calculate the stroke, a speed or an acceleration speed of the linear compressor, and a microcomputer inputting a switching signal for controlling the voltage applied to the linear compressor into the switching device to make a present stroke follow an initial stroke reference.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.